HISTOGENESIS OF THE PULMONARY-LESIONS IN THE COURSE OF VISNA MAEDI VIRUS-INDUCED PNEUMONIA

The major characteristic lesion observed following spontaneous infecti on of sheep by the prototype lentivirus, maedi-visna virus (MVV), is a lymphocytic intestitial pneumonia. Similar lesions may be observed wi th variable frequency following infection of other species by pathogen ic lentiviruses, for example in children infected by HIV-1. Further, l entivirus-induced lesions involving organs other than the lungs freque ntly involve a comparable cellular infiltration. The cellular composit ion of bronchoalveolar lavage specimens from naturally- or experimenta lly-infected sheep has been examined with a view to describing the pat hological progression of lentivirus-induced lung lesions. The naturall y-infected sheep presented advanced lesions typical of 'maedi', while the experimentally-infected newborn lambs permitted the study of early lesions which we refer to as 'pre-maedi'. In both cases there was a c onsiderable infiltration of lymphocytes, predominantly CD8+ in maedi, but with nearly equal numbers of CD4+ cells in pre-maedi. A large prop ortion of the alveolar lymphocytes in spontaneous maedi, but not in ex perimentally-infected lambs, express high levels of MHC class II antig en, suggesting an activated phenotype. Activated macrophages, the chie f target cells for MVV infection, are also present at this advanced st age of the disease suggesting the involvement of mediators such as IL- 8 in the cellular interactions leading to the localization of particul ar lymphocyte sub-populations in the pulmonary parenchyma during lenti viral disease.